Wireless local area network (WLAN) systems may be formed by one or more access points (APs) that provide a shared wireless medium for use by a number of client devices or stations (STAs) to exchange data with each other and/or with devices external to the WLAN system. To improve data throughput, the shared wireless medium may be divided into a primary channel and one or more secondary channels. The primary and secondary channels may be of various bandwidths, for example, by bonding a number of 20 MHz-wide channels together to form 40 MHz-wide channels, 80 MHz-wide channels, and/or 160 MHz-wide channels.
In a typical WLAN, only one STA may use the wireless medium at any given time, and each STA may be associated with only one AP at a time. To prevent multiple STAs from accessing the shared wireless medium at the same time (which may result in collisions), STAs may contend with each other for access to the wireless medium or channel. Channel access mechanisms may be classified as either static or dynamic. In general, static channel access (SCA) mechanisms attempt to gain access to the entire bandwidth of the wireless medium, while dynamic channel access (DCA) mechanisms attempt to gain access to an available portion of the bandwidth of the wireless medium.
More specifically, a STA using an SCA mechanism typically attempts to transmit data using both the primary and secondary channels of the WLAN. If the secondary channel is busy, then the STA typically defers channel access (e.g., even if the primary channel is available) until the entire bandwidth is available. Thus, although SCA mechanisms may ensure maximum throughput by only using the entire frequency spectrum of the WLAN, frequent medium access deferrals resulting from traffic or interference on the shared wireless medium may reduce channel utilization.
In contrast, while a STA using a DCA mechanism may initially attempt to gain access to both the primary and secondary channels of the WLAN, if the secondary channel is busy and the primary channel is available, the STA may dynamically adjust its transmission bandwidth, for example, to begin data transmissions on the primary channel. Thus, although DCA mechanisms may not always achieve maximum throughput, medium utilization is improved (e.g., as compared with SCA mechanisms) by initiating data transmissions even when only the primary channel is available.
Wireless devices such as APs and STAs may use MU-MIMO communications to increase data throughput by transmitting multiple spatial streams to multiple users at the same time. However, hardware constraints may limit the ability of wireless devices to use conventional DCA mechanisms for MU-MIMO communications. As a result, wireless devices that utilize MU-MIMO communications may be limited to software-based SCA mechanisms, which as mentioned above may undesirably reduce utilization of the wireless medium. Thus, there is a need for wireless devices to dynamically adjust the bandwidth for MU-MIMO communications, for example, to improve medium utilization.